#app{
  display: flex;
  align-items: center;
  justify-content: center;
  height: 100vh;
}

.progress-1 {
  width:6rem;
  height:1rem;
  /* background:linear-gradient(#000 0 0) 0/0% no-repeat; */
  background-image: linear-gradient(#000 0 0);
  background-color: #ddd;
  background-repeat: no-repeat;
  background-size: 0%;
  background-position: 0%;
  animation:p1 2s infinite linear;
}
@keyframes p1 {
    100% {background-size:100%}
}